Chikungunya and dengue are important viral diseases that affect over 50 million people each year in the tropical and subtropical areas of the world. The chikungunya and dengue viruses evolved in non-human primates in the forests of Africa and Asia where forest mosquitoes maintained the viruses in a monkey-to-monkey (sylvatic) transmission cycle. It is only in the last few hundred years that the viruses began to infect people and their domestic and peri-domestic mosquitoes and be maintained in a human-to-human (urban) transmission cycle. A lot is known about the human mosquitoes that carry dengue and chikungunya and control programs have been developed to try and prevent and control infections. Unfortunately, there is little data on the roles wild non-human primates and their mosquitoes play in transmission cycles as they are mainly found in relatively remote areas which lack local infrastructure and facilities for research. On the small Caribbean island of St Kitts, however, there is a large population of wild African green monkeys which are ubiquitous and relatively easy to study. Also, the island is easily accessible and has very good infrastructure and research facilities for the study of dengue and chikungunya which both occur on St Kitts. To investigate the role African green monkeys on St Kitts may play in sylvatic and urban transmission cycles of chikungunya and dengue viruses we intend to trap mosquitoes from each of the five well demarcated ecosystems on the island over two years to determine the mosquitoes present and their temporal and spatial distribution patterns. Pools of the mosquitoes will be tested for the presence of dengue and chikungunya viruses to determine which species are infected and hence likely vectors, and also where on the island infections are most common. Blood meals from fed mosquitoes will be analyzed by PCR to determine the animal hosts on which the different mosquito species feed, in particular monkeys and people. African green monkeys from the five ecosystems on the island will be tested for antibodies against dengue and chikungunya viruses to determine the pattern of exposure on the island. Together, this information will indicate if the African green monkeys on St Kitts might be involved in sylvatic and urban transmission cycles of dengue and chikungunya viruses and whether non-human primates might be important in the epidemiology of dengue and chikungunya in other parts of the world, notably Africa, Asia and South America, where people live in close proximity to wild populations of non-human primates.